Energy of building complexes is often supplied by local utility plant, which converts energy from public resources to utilities needed in the building complex. Economically optimal scheduling of such a utility plant or a microgrid (from now on ‘controlled plants’) operation with complex internal structure consists in determination of set points of plant energy conversion devices, so that energy demands of the building complex are satisfied and plant operating costs are minimal. The solution is usually applied in fixed intervals usually 15 minutes to 60 minutes long, where the energy demands and the conversion characteristics are considered fixed.
In reality energy demand varies within these periods and there has to be a lower level controller that strives to balance energy supply and demand and ensures satisfactory operation of the whole system. The balances are of two types—hard balance that must be always satisfied (e.g. electricity supply and demand) and soft balance, which may be temporarily violated, such as heat delivery to building heating system may be less than needed for some time. The utility plant structures may be complex, and therefore, allocation of required production changes to cover demand changes can be complex.
Currently a fixed sequence of switching on and off energy producing devices is used to reach the balance when the demand significantly changes. For example, a first boiler in a set of boilers is first set to reach balance. If the first boiler in the set reaches its maximum allowed heat output and balance is not reached. a next boiler is switched on and changed, followed by the next in the list, until balance is finally reached.